docs: def _master_key_provider() -> KMSMasterKeyProvider:
      """Build the V0 master key provider."""
      master_key_provider = KMSMasterKeyProvider()
      master_key_provider.add_master_key_provider(NullMasterKey())
      master_key_provider.add_master_key_provider(CountingMasterKey())
      return master_key_provider